CODEWITHSUNDEEP
djangodjango-rest-framework
shafayat hossain
shafayat hossain

Reputation: 1129

django rest framework get() returned more than one object though filter() method is used

In model.py, I've two models

class student(models.Model):
    name = models.CharField(max_length=255)
    registration_number = models.CharField(max_length=255)
    session = models.CharField(max_length=255)
    college = models.ForeignKey(to='college', on_delete=models.CASCADE)

    class Meta:
        db_table = 'student'


class semester(models.Model):
    semester = models.IntegerField()
    student = models.ForeignKey(to='student', on_delete=models.CASCADE)
    sgpa = models.FloatField()
    grade = models.CharField(max_length=255)
    is_fail = models.BooleanField(default=True)

    class Meta:
        db_table = 'semester'

Serializer classes looks like

class SemesterSerializer(serializers.ModelSerializer):
    class Meta:
        model = models.semester
        fields = ('id', 'semester', 'sgpa', 'grade', 'is_fail',)

class StudentSerializer(serializers.ModelSerializer):
    class Meta:
        model = models.student
        fields = ('id', 'name', 'registration_number', 'college', 'session',)

and views.py contains

class SemesterViewSet(viewsets.ModelViewSet):    
    def get_queryset(self):
        if 'semester' in self.kwargs:
            return models.semester.objects.filter(semester=self.kwargs['semester'])
        else:
            return models.semester.objects.all()

    lookup_field = 'semester'
    serializer_class = serializer.SemesterSerializer

url patterns are

router = DefaultRouter()
router.register('semester', views.SemesterViewSet, base_name='semester')
urlpatterns = [
    url(r'', include(router.urls)),
]

When I tried to visit url/semester/8, MultipleObjectsReturned exception raised and showes get() returned more than one semester -- it returned 2! error message. Here I've not used any get() method. Why this is happening and what is solution? I need to show all result of semester.

Upvotes: 1

Views: 1966

Answers (1)

JPG
JPG

Reputation: 88609

Remove lookup_field from view or change it to lookup_field = 'id'
The error is because while you calling a retrieve() method, inside it invokes a get_object() which is sililar to the query similar to 

semester.objects.get(semester=semester.objects.get(id=8).semester)


semester.objects.get(lookup_field=parameter)

example:

semester.objects.get(semester=8)


So, if there is more than 1 semester instances have same semester value, it would raise an error

UPDATE-1
Try to override retrieve() method in view,

from rest_framework.response import Response


class SemesterViewSet(ModelViewSet):
    def get_queryset(self):
        if 'semester' in self.kwargs:
            return semester.objects.filter(semester=self.kwargs['semester'])
        else:
            return semester.objects.all()

    lookup_field = 'semester'
    serializer_class = SemesterSerializer

    def retrieve(self, request, *args, **kwargs): # Change is here <<
        serializer = self.get_serializer(self.get_queryset(), many=True)
        return Response(data=serializer.data)

Upvotes: 4

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